The cell utilizes a variety of pathways and signaling cascades to repair DNA damage; however, how the genome is repaired when DNA is actively replicating is imperfectly understood. DNA repair during replication contributes to chemotherapeutic resistance while compromised repair during replication is responsible for many rare genetic diseases. Replication fork remodeling is a key intermediate in damage-associated repair during replication, however which proteins are responsible for fork regression and subsequent resolution of regressed intermediates to facilitate restart remains unknown. This project will test the roles and redundancy of two candidate helicases, Marcal1 and Blm, in replication fork remodeling (a key intermediate in repair) using classical Drosophila genetics as well as modern molecular techniques. Blm helicase has functions in homologous recombination repair of double-strand breaks. Preliminary data suggests that Blm may be differentially regulated in replication-related functions vs. HR roles; this may affect Top3? interactions, which are necessary for HR functions. This hypothesis will be tested through characterization of Blm-Top3? binding in replication using standard techniques. Lastly, Blm has also been implicated in facilitating replication progression through repetitive regions. This novel role will be tested usig innovative assays in Drosophila embryos in conjunction with molecular techniques. The combined approach of this project is designed to clarify complex data interpretation resulting from partial redundancy of repair pathways and proteins. This project will provide insight into how replication and repair pathways work together to preserve genomic stability with the potential to impact rare disease treatment as well as chemotherapeutic design.